Work feed devices for centreless grinding machines

ABSTRACT

A work feed device for a centreless grinding machine comprises a cylinder housing a pusher piston, rigid with a workpiecesupporting shoe and a control piston. The control piston is linked to the pusher piston by resilient means in the form of a cushion of compressed gas and by a telescopic element which determines the maximum spacing between the pistons. The pressure of the compressed gas is adjustable.

United States Patent Inventor: Georges Garcin, Cran-Gevrier,

France Assignee: Ste Nouvelle de Roulements (S.N.R.), Annecy, France Filed: Nov. 10, 1972 App]. No.: 305,347

[30] Foreign Application Priority Data Dec. 27, 1971 France 71.46832 References Cited UNITED STATES PATENTS 2,086,024 Flygare f. 51/238 S Garcin Nov. 19, 1974 [54] WORK FEED DEVICES FOR CENTRELESS 3,032,935 5/1962 Lockwood 51/236 X GRINDING NES R24,202 8/1956 Blood 51/103 WH Primary ExaminerAl Lawrence Smith Assistant ExaminerMarc R. Davidson Attorney, Agent, or FirmC1e|le W. Upchurch [57] ABSTRACT A work feed device for a centreless grinding machine comprises a cylinder housing a pusher piston, rigid with a workpiece-supporting shoe and a control piston. The control piston is linked to the pusher piston by resilient means in the form of a cushion of compressed gas and by a telescopic element which determines the maximum spacing between the pistons. The

pressure of the compressed gas is adjustable.

7 Claims, 2 Drawing Figures l2 l6 2/ 27 I514 73 ll 18 I so a thrust is exerted on the workpiece, the thrust being WORK FEED DEVICES FOR CENTRELESS GRINDING MACHINES BACKGROUND OF THE INVENTION 1. Filed of the Invention The present invention relates to work feed devices for centreless grinding machines.

2. Description of the Prior Art 1 It has been proposed to use mechanical feed devices for grinding machines, in which devices the feed rate is constant whatever the cutting power of the grinder and the conditions of grinding. The result is that, with these devices, optimum machining is not always achieved and there is a loss of time when grinding work pieces of reduced size.

Feed devices have also been proposed in which the whole of the machine table, which is very heavy, is advanced. However, the inertia is quite considerable with respect to the cutting stresses. Furthermore, resonance phenomena arise which make it necessary to use dampers.

SUMMARY OF THE INVENTION According to the present invention, the device comprises a cylindrical body in which are slidingly mounted a pusher piston which is rigid with one of the shoes which support the piece to be ground, a control piston linked to the said pusher piston by resilient means, the force of which is regulable, and by a telescopic retaining element limiting the maximum spacing between the two pistons.

Preferably a workpiece to be ground, having been taken over by a support face by virtue of an eccentric arrangement and rotation, becomes centred on the shoes. When the control piston is pushed onto a forward stop, the pusher piston carrying the shoe, connected with the control piston by virtue of the telescopic retaining element and the resilient means, also moves forward, pushing the workpiece so that it contacts the grinder.

When the control piston has moved forward by a distance greater than that travelled by the pusher piston, this latter becomes detached from the telescopic retaining element which links it to the control piston and transmitted to the workpiece by the resilient meansand being readily varied if desired during the course of grinding.

This thrust can for example be regulated so that it is very low at the moment of contact between the workpiece and the grinder to avoid deterioration of the grinder on the rough workpiece, the thrust increasing progressively to reach its maximum when the workpiece is smoothed. The workpiece is thus accurately ground, without any impact, and wear on the grinder is minimal.

Forward feed of the pusher piston is limited by a stop, the contact of which with the said piston can be indicated by various detecting means which are known per Thus, it is possible at this moment to control smoothing by means of a timing device, or to give this stop a return movement for execution of finishing and smoothing. In this case, finishing is carried out at a control speed and is therefore no longer dependent upon the oscillation between the grinder and the workpiece. It is likewise possible to control the return and stopping of the stop by a feeler gauge. When smoothing is finished, the whole returns to the rear stop position and when the workpiece is released from the grinder, it may be removed so as to allow a new workpiece to be accepted.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a longitudinal section of a workpiece feed device in accordance with the invention, the device being shown in its configuration prior to a grinding operation; and

FIG. 2 is a section similar to FIG. 1 but showing the device during smoothing of a ground workpiece.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1 and 2 a workpiece in the form of a ring 20 or other rotatable body is mounted on takeover. means of a grinding machine which comprises a magnetic support face 3, a shoe2 which is mounted to pivot about a spindle 24 on a support element 25 which is fixed, and a shoe 1 which is mounted to pivot about a spindle 26 on an end portion of a pusher piston 5 this latter shoe being a so-called 3-hour shoe. The work piece 20, which is engageable by a grinder in the form of a grinding wheel 4, rests on the face 3 and on the shoes 1 and 2; the workpiece 20 follows the shoe 1 during its return movement while being supported on the shoe 2 and on the magnetic face 3.

The workpiece feed device comprises a cylindrical body 12 in which are slidingly mounted the pusher piston 5 which carries the shoe 1, and a control piston 6 connected to operating means, not shown in the drawings, and capable of communicating to the piston 6 a displacement according to the double-headed arrow F, F! I Provided between the pistons 5 and 6 in the cylindrical body 12 is a chamber 19 enclosing a cushion of compressed air, the chamber 19 being connected to a source of compressed air by port 11. This cushion of compressed air repels the pistons 5, 6 in relation to each other and enables the control piston 6, during its movement, to be rendered rigid with the pusher piston 5.

Between the pistons 5 and 6 is a telescopic retaining element 7 which at one of its ends has a plate 21 which is screwed and locked in a threaded bore 27 of the pusher piston 5 and has at its other end a head 14 which is mounted to slide in a bore 13 of the control piston 6.

The distance separating the pusher piston 5 from the control piston 6 is limited by the head 14 of the telescopic'retaining element 7 which is arranged to abut the end portion of stop screws 15 which are carried by the control piston 6. A spindle 28 slidable eoaxially within the retaining element 7 has a head 28a arranged to contact a sensor 29 of a feeler 9 mounted in the control piston and linked with smoothing control means.

The other end of the spindle 28 is arranged to contact circular abutment means 8 located in a bore 30 in the piston 5 and eccentrically keyed on a spindle 23 jour- V to each other and which slide on the spindle 23 during axial displacement of the piston 5 whereby to maintain the piston in a specific angular position.

The spindle 23 extends on one side to the exteriorof the cylindrical body 12 and enables the abutment means 8 to be given a selected angular displacement.

The bore 31 in the cylindrical body 12, inside which the pistons 5 and 6 slide, comprises a helical oil groove 16 which discharges into a concentric groove 17 in a forwards direction and into a concentric groove 18 in the rearwards direction. Escape of greasy air occurs at the two ends of the bore 31, so avoiding the ingress of foreign bodies. Greasy air flows through the oil groove 16 to provide an aerostatic suspension to the pistons 5 and 6 in the bore 31 of the cylindrical body 12, and thus to permit movement of the pistons with very low friction.

When a workpiece 20 has been located as described hereinabove and when the grinding wheel 4 is in position as shown in FIG. 1, means provided in the machine on which this work feed device is mounted move the control piston 6 in the direction of the arrow F until a head of the piston 6 abuts against the rear end of the cylindrical body 12. The pusher piston S which is subject to the action of the cushion of compressed air within the chamber 19 follows the forwards movement of the control piston 6, whereby the shoe 1 contacts the workpiece 20 and urgesit against the grinding wheel 4 with a pressure equal to the pressure of the air cushion in the chamber 19. v

' This pressure is low at the moment of contact between the workpiece 20 .and the grinding wheel 4 in order to prevent the surface of the grinding wheel from being damaged by the workpiece which initially has a rough surface, the pressure increasing progressively to reach a suitable contact pressure. These regulations and variations of pressure, effected by known means, make it possible to achieve a maximum working speed without damage to the ground surface.

' Forwards movement of the control piston 6 exceeds that 'of the pusher piston 5 since movement of the latter ceases when the workpiece 20 contacts the grinding wheel 4, and thus the stop screws move away from the head 14 of the telescopic retaining element 7 as illustrated in FIG. 2. The retaining element 7'is accordingly free to move axially in the bore 13 of the control piston 6.

If the bore in the workpiece which is to-be ground has some irregularities (for example if the bore is oval, triangular, or eccentric) each time an irregularity is encountered there occurs a slight return movement of the workpiece 20 and thus of the piston 5. By virtue of the low inertia of the assembly, the pressure exerted on the grinding wheel 4 by the irregularities is only very slightly increased and the workpiece becomes progressively smoothed.

The forward feed of the pusher piston 5 ceases when the plate 2.1 of the retaining element 7 contacts the eccentric abutment means 8. Since the spindle 28 is likewise braced against the abutment 8, it is displaced slightly rearwardly and its head 28a contacts the sensor 29 of the feeler 9 which detects the position of the piston 5 and controls the smoothing operation, this position beingmaintained for a period of time predetermined by a timing device. Then the feeler controls the return movement of the piston 5 and that of the ground workpiece 20 which follows the shoe 1 as described before.

By rotating the eccentric abutment means 8 through a selected angle, it is possible to correct the dimensions or to control the rotation of this abutment for finishing and smoothing, particularly in the casewhere a feeler gauge senses the removal of material from the workpiece being ground.

The feed device described has a low inertia and al- 10 lows the grinding wheel to follow the entire surface of the workpiece What is claimed is: p 1. In a centreless grinding machine means defining a support face for a workpiece, a shoe for supporting the workpiece radially, and a workpiece feed device, said feed device comprising cylinder means, a first piston mounted in the cylinder means and carrying the shoe 20 a second, control piston mounted in the cylinder means,

resilient means connecting the second piston to the first piston and applying an adjustable force between the pistons, and

a telescopic retaining element, said element limiting the maximum spacingbetween the pistons. 2. A grinding machine as claimed in claim 1, wherein the pistons and cylinder means define a chamber therebetween and the resilient means comprises a cushion of compressed gas within the chamber, the pressure of the compressed gas being variable and the chamber being connected to. a source of compressed gas.

3. A grinding machine asclaimed in claim 1, wherein the telescopic element has opposed end portions, one

3 5 of the end portions being secured to the first piston, the

other end portion including head means, the head means being slidable in the second piston, and the second piston including abutment means for the head means, the abutment 40 means limiting movement of the said element.

a spindle journaled in the cylinder means, the circular element being eccentrically mounted on the spindle, and the first piston including slots, the spindle extending through the slots.

6. A grinding machine as claimed in claim 4, wherein the said feed device further comprises feeler means for controlling a smoothing operation and return movement of the first piston, said feeler means being housed in the second piston and including sensor means, and

spindle means, said spindle means being slidable in the retaining element and being arranged to engage the abutment means, and sensor means engaging the spindle means when the spindle means engages the abutment means.

7. A grinding machine as claimed in claim 1, wherein the first piston is aerostatically suspended. 

1. In a centreless grinding machine means defining a support face for a workpiece, a shoe for supporting the workpiece radially, and a workpiece feed device, said feed device comprising cylinder means, a first piston mounted in the cylinder means and carrying the shoe a second, control piston mounted in the cylinder means, resilient means connecting the second piston to the first piston and applying an adjustable force between the pistons, and a telescopic retaining element, said element limiting the maximum spacing between the pistons.
 2. A grinding machine as claimed in claim 1, wherein the pistons and cylinder means define a chamber therebetween and the resilient means comprises a cushion of compressed gas within the chamber, the pressure of the compressed gas being variable and the chamber being connected to a source of compressed gas.
 3. A grinding machine as claimed in claim 1, wherein the telescopic element has opposed end portions, one of the end portions being secured to the first piston, the other end portion including head means, the head means being slidable in the second piston, and the second piston including abutment means for the head means, the abutment means limiting movement of the said element.
 4. A grinding machine as claimed in claim 1, wherein the feed device further comprises abutment means mounted within the first piston and rigid with the cylinder means, and wherein the retaining element is arranged to engage the abutment means.
 5. A grinding machine as claimed in claim 4, wherein the abutment means comprises a circular element, said feed device further comprising a spindle journaled in the cylinder means, the circular element being eccentrically mounted on the spindle, and the first piston including slots, the spindle extending through the slots.
 6. A grinding machine as claimed in claim 4, wherein the said feed device further comprises feeler means for controlling a smoothing operation and return movement of the first piston, said feeler means being housed in the second piston and including sensor means, and spindle means, said spindle means being slidable in the retaining element and being arranged to engage the abutment means, and sensor means engaging the spindle means when the spindle means engages the abutment means.
 7. A grinding machine as claimed in claim 1, wherein the first piston is aerostatically suspended. 